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Crispian Mills is the son of Hayley Mills and the director Roy Boulting, the grandson of Sir John Mills and Mary Hayley Bell, thus being a scion of the thespian dynasty which the critic David Thomson nastily characterised in his Biographical Dictionary of Cinema as possessing “insipid, tennis-club talent”.

Crispian Mills found success in the Nineties as the frontman of indie rock band Kula Shaker — their debut album K went double platinum, although they later had problems when Mills unwisely told the NME “I love the swastika” — for its mystical connotations, he meant. They reformed a few years ago and released a well-reviewed album, Pilgrims Progress, in 2010 but then postponed other projects while Mills worked on this movie.

A Fantastic Fear of Everything, which he has both written and directed, is Mills’s film debut and it is the worst movie I have ever reviewed. It’s not a strong week, in the wake of Prometheus, but even so, this came as a shock. Most films, however feeble, have some little element you like — an actor in a minor role you fancy, a glimpse of a beautiful landscape, one inventive line of dialogue, maybe a tune. Fantastic Fear (to cut it short) not only has no such relief but quite ruthlessly ticks off the box for everything you least want to see, beginning with its charisma-bypassed star Simon Pegg and progressing through gangsta rap, therapy-speak and incessant smoking.

Pegg plays Jack, a former children’s writer now working on Decades of Death, a book about Victorian serial killers, while collapsing into paranoia and squalor in a dark, dirty flat in Hackney, believing all the murderers are out to get him.

When his agent tells him a Hollywood producer would like to meet him that evening, Jack is thrown into even greater disarray because he has no clean clothes and a phobia of launderettes, linked to his abandonment in one as a child.

Getting us thus far takes about an hour and, apart from a scene with his agent and another with his therapist, we see only Pegg, in his dingy flat, in his saggy underpants, a sight nobody would be subjected to in a civilised society. It’s cruel and unjust punishment. It’s like Ed Reardon’s Week gone really wrong.

There’s a long gag about Jack trying to dry some clothes in the oven but which catch fire. Then he goes to a launderette, for the second half of this not short film. There, he and a pretty Indian girl (Amara Karan), also doing her washing, are kidnapped by a deranged community policeman, shackled in a cellar beneath the launderette, and told they will be killed when the spin cycle is over. But Jack tells the loony copper one of his children’s stories, about how Harold the Hedgehog overcame his fear of abandonment in a scary wood (the film switching into Oliver Postgate-style animation for this). The madman is entranced, they bond over their shared fears (“you’re like me, we were both abandoned, we’re the same”) and all is well. That’s it.

There is a complete failure of tone in this film, from begining to end. It is ridiculous but it wants to be taken seriously. It believes itself to be funny but it never raises a single laugh. It is never remotely plausible yet on it goes. It is not, by the way, one of those films that is so bad it comes out the other side to being kitschly enjoyable.

You begin, quite early on, to wonder how the film got made, why nobody said anything or called a halt to proceedings from simple kindness. A question too sad to insist on, perhaps.

There is always an answer, however, and always it goes back to the past. Crispian Mills, now coming up for 40, had a troubling childhood. His mother, a child star, was 33 years younger than his father, whose fourth wife she was. They got divorced when their son was four and he did not see his father again until he was 16. The film’s themes doubtless draw on his own traumas.

That doesn’t make it of any use to anyone else, except perhaps as a striking example for film studies courses of how not to do it. As for Crispian Mills himself, he clearly should not make more movies and might think about undertaking some humdrum, useful and less expressive work. Picking up litter in Finsbury Park for a year or two? It is awfully messy.